This invention relates to a traffic signal system for blind people and, more particularly, to such traffic signal system which serves to safely guide blind people by emitting sound such as birds songs and melodious sounds.
Heretofore, such traffic signals for blind people have been arranged so that imitation sound such as birds songs or melodious sounds is emitted at a certain fixed level. Therefore, when the traffic is busy, the imitation sound is masked by the surrounding noise to such an extent that blind persons on the verge of crossing the road experience difficulty in hearing and identifying the signal sound. On the contrary, when the traffic volume and the surrounding noise level go lower, for example, at night the imitation sound becomes highlighted, consequently giving rise to an environmental noise problem of putting great annoyance to those people living near the signal device.
To eliminate such inconvenience, it may be devised to measure the surrounding noise and to produce imitation sound at a proper volume corresponding to the measured noise level. For this purpose, a microphone is used to detect the surrounding noise level so that a speaker may emit sound having a volume proportional to the detected noise level. However, it is sometimes difficult to newly install conductors or cables exclusive to signal devices for the blind to electrically interconnect the signal devices. In these cases, signal devices should independently detect noise and emit imitation sound at a proper volume.
Therefore, an object of this invention is to provide a traffic signal system for blind people in which the volume of signal sound can be controlled in accordance with the surrounding noise level.
Under these conditions, although imitation sound signal generator circuits produce electric sound signals which have the same cycle for all the signal devices located in one direction of a crossing, the actual time of generating imitation sound and the reverberation of speakers may vary from one signal device to another. Also, a substantial time is required for the sound emitted from a speaker of the traffic signal device on one side of the road to propagate through the air and reach the signal device on the opposite side. As a result, the imitation sound emitted from the speaker on one side may be caught by the microphone on the opposite side of the crossing at the beginning of the subsequent quiescent time of imitation sound generation. The signal device which detects the sound originated from the opposite speaker in addition to the surrounding noise to be detected increases its output level. Further, since a large volume of sound emitted from the signal device on one side is accompanied with reverberation having a high sound pressure, the signal device on the opposite side receives this reverberation and thus inevitably and undesirably raises its output level.
Accordingly, another object of the present invention is to provide an improved traffic signal system for blind people, in which a detected surrounding noise signal is fed to an automatic volume control unit with a delay from the instant when an imitation sound signal generator circuit becomes quiescent, so that the volume of imitation sound can be controlled without any disturbance by the imitation sound emitted from other associated signal systems.